In the United States over 20 million people are engaged in the pursuit of physical exercise and/or physical therapy. These exercises fall into two general categories, aerobic exercise and strength conditioning. Many strength exercise routines require that the resistance to exercise be changed at various times. In most instances this requires the user to stop exercising and engage in some selection process to manually adjust a mechanical setting to change resistance parameters (such as inserting a pin to select a specific number of weight plates, adding or subtracting elastic devices, turning a knob which varies pneumatic or hydraulic resistance, etc).
U.S. Pat. No. 4,650,185 to Cartwright describes an exercise machine which attempts to provide a solution to this problem. The Cartwright device provides a beam pivoted off center with a weight movable along the beam under control of a motor. The drawback of this device is that the range of motion of the lever is only 90 degrees and in order to traverse a 40 inch span of travel, the length of the lever required would be four feet. This requires more space to operate than is acceptable in most home or gym settings.
Another attempt to solve this problem is described in U.S. Pat. No. 5,624,353 to Naidus. Naidus describes a weight training machine which comprises a variable resistance capability. However, this device requires the use of two sources of resistance to provide the variability of the resistance and the primary force must be manually selected.
U.S. Pat. No. 5,344,374 to Telle describes another variable resistance exercise machine. Telles device includes the combination of a pivotally mounted linear actuator and a dampener member, both of which are adjustable. Telle's device, like Cartwright's is unwieldy and impractically large and space consuming.